Landfills typically produce landfill gas (LFG) as a result of decomposition processes of organic waste, and methane is often a component of LFG. In order to reduce emissions of methane and other contaminants in LFG, the landfill sites are typically capped with a layer of cover material and gas extraction systems are installed to pull LFG out before it can penetrate the cover layer and escape. At larger sites, these gas extraction systems can consist of a plurality of vertical and horizontal wells drilled or constructed into the landfill, which are connected with piping to one or more vacuum sources. The cover layer prevents gas from freely escaping, while the vacuum in the extraction wells pulls LFG into the collection system. LFG extraction wells typically have a manual valve that adjusts the localized vacuum pressure in that well, as well as a set of ports for sampling the gas characteristics with a portable gas analyzer. Landfill gas is most often disposed of in a flare, processed for direct use, or used to power electricity generation equipment (such as generators or gas turbines).
The horizontal and vertical wells in the collection system typically consist of a length of perforated pipe connected to a length of solid pipe that rises through the surface of the landfill for wellhead access. The perforated pipe may be laid across the landfill during active dumping and subsequently buried (forming “horizontal wells”) under additional lifts or inserted into a hole drilled through the landfill (traditional “vertical wells”). This pipe then acts as the gas extraction interface between the fill and the collection system. Additional extraction points may also exist, with collection through leachate cleanouts, sumps, cisterns, temporary cover layers, and other points of fluid connection with the landfill mass.